Micromechanical study of the Scale Effect on composite material laminates

Abstract

From the beginning of the application of composite materials, different theories to predict their behaviour and failure have been developed. The authors have already made a previous study, analyzing at the macroscopic level (both from an experimental and theoretical point of view), the failure of non-conventional laminates changing the thickness of the laminas that form it, in order to evaluate the “scale effect” (also known as “in-situ strength”) present in them. Results of this study proved the strength variation of the laminate with its configuration (scale effect) and it was found that the presence of laminas with fibres oriented in the direction of the load diminishes this effect. This paper is focused on the understanding of the aforementioned effect, conducting a study at  micromechanical level (the level where the damages leading to the failure are generated) of the scale effect with an energetic approach, in order to progress in the understanding of this phenomenom. To this end, the Boundary Element Method (BEM) has been used. It has been applied to a laminate model with [0, 90n]S stacking sequence, where the influence of n at different stages of the generation and progression of damage has been studied: the beginning of the damage (that takes place when the debonding between fibre and matrix happens) and during the change of direction of the debonding crack towards the matrix (kinking). The models developed are multiscale, involving a mesoscale representation of the laminas of the laminates (modelled as homogeneous) and with micromechanics cells that simulate fibre and matrix and therefore with the capacity for collecting information about damage mechanisms observed experimentally.

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